[fix] do not warn if module variables are not the only dependencies in reactive statements (#6510)

The warning was too strict, since there are valid use cases for having non-reactive variables inside reactive statements
Fixes #5954

Author: tanhauhau

src/compiler/compile/Component.ts

@@ -1192,6 +1192,7 @@ export default class Component {
 				const assignees = new Set<string>();
 				const assignee_nodes = new Set();
 				const dependencies = new Set<string>();
+				const module_dependencies = new Set<string>();
 
 				let scope = this.instance_scope;
 				const map = this.instance_scope_map;
@@ -1228,7 +1229,7 @@ export default class Component {
 									variable.is_reactive_dependency = true;
 									if (variable.module) {
 										should_add_as_dependency = false;
-										component.warn(node as any, compiler_warnings.module_script_variable_reactive_declaration(name));
+										module_dependencies.add(name);
 									}
 								}
 								const is_writable_or_mutated =
@@ -1253,6 +1254,10 @@ export default class Component {
 					}
 				});
 
+				if (module_dependencies.size > 0 && dependencies.size === 0) {
+					component.warn(node.body as any, compiler_warnings.module_script_variable_reactive_declaration(Array.from(module_dependencies)));
+				}
+
 				const { expression } = node.body as ExpressionStatement;
 				const declaration = expression && (expression as AssignmentExpression).left;
 

src/compiler/compile/compiler_warnings.ts

@@ -20,9 +20,9 @@ export default {
 		code: 'non-top-level-reactive-declaration',
 		message: '$: has no effect outside of the top-level'
 	},
-	module_script_variable_reactive_declaration: (name: string) => ({
+	module_script_variable_reactive_declaration: (names: string[]) => ({
 		code: 'module-script-reactive-declaration',
-		message: `"${name}" is declared in a module script and will not be reactive`
+		message: `${names.map(name => `"${name}"`).join(', ')} ${names.length > 1 ? 'are' : 'is'} declared in a module script and will not be reactive`
 	}),
 	missing_declaration: (name: string, has_script: boolean) => ({
 		code: 'missing-declaration',

test/validator/samples/reactive-module-variable-2/input.svelte

@@ -0,0 +1,7 @@
+<script context="module">
+	let PI = 3.14;
+</script>
+<script>
+	let r;
+	$: area = PI * r * r;
+</script>

test/validator/samples/reactive-module-variable-2/warnings.json

@@ -0,0 +1 @@
+[]

test/validator/samples/reactive-module-variable/warnings.json

@@ -2,15 +2,15 @@
 	{
 		"code": "module-script-reactive-declaration",
 		"message": "\"foo\" is declared in a module script and will not be reactive",
-		"pos": 65,
+		"pos": 59,
 		"start": {
-			"character": 65,
-			"column": 10,
+			"character": 59,
+			"column": 4,
 			"line": 5
 		},
 		"end": {
-			"character": 68,
-			"column": 13,
+			"character": 69,
+			"column": 14,
 			"line": 5
 		}
 	}